No mention of them yet in any of the press information that I've seen.
However, last year they were not mentioned either, until long after all the holiday press releases were out. So anything is possible.
It was a nice surprise that they were back last year -- they put on a great show. Any additional live entertainment is wonderful (even if Epcot it probably the park that needs it the least). Would it kill anyone to have regular performances by a special live group in the MK, for instance? Carolers? Bands? Anything?